<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  .box {
    width: 100px;
    height: 100px;
    padding: 50px;
    /* box-sizing: border-box;      */
    /* 盒子会包含边框，内边距*2小与宽度，不会撑大盒子 */
    background-color: aqua;
}
.box1 {
    width: 100px;
    height: 100px;
    /* 默认是content-box，当设置padding时，会撑大盒子 */
    background-color: firebrick;
}
.parent {
  width: 200px;
  height: 200px;
  background-color: red;
  .child {
    width: 100px;
    height: 100px;
    background-color: pink;
    margin: 50px;
    /* visibility: hidden; */
    /* opacity:0 */
    /* display: none; */
    /* width: 0;
    height: 0; */
    position: absolute;
    top: 100vh;
    overflow: hidden;

  }
}

</style>
<body>
  <!-- <div class="box">123</div>
  <div class="box1">123</div> -->
  <div class="parent">
    <div class="child"></div>
  </div>

</body>
</html>